Field of the Invention
The present invention relates to a camera module, and more particularly, to an apparatus and method for controlling auto focus of a camera module including a voice coil motor actuator.
Discussion of the Related Art
Owing to the recent technical developments, multi-functional mobile terminals having various functions intensively integrated therein are released and mobile terminals tend to be downsized and lightened to fit the mobile environments despite functional complexity and diversity.
Therefore, a camera module installed in a mobile terminal such as a mobile phone, a laptop or the like tends to be downsized owing to the ultra-downsizing and ultra-precision of lenses.
An optical system of a camera module needs an auto-focus function to have a clear view of a target object that becomes a subject.
Such an auto-focus function uses actuators of various types in order to move a lens module to an optical focal position. And, performance of an auto-focus of a camera module can vary according to property of an actuator configured to transport a lens module.
Auto-focus actuators can include actuators of various types such as a voice coil motor (VCM) actuator, a piezo-electrically driven actuator, an MEMs actuator driven by static capacitance and the like.
With respect to a camera module that employs a voice coil motor actuator, permanent magnet is located at a fixing part of the camera module and a coil is attached to a lens module to be driven, whereby a magnetic circuit is configured. Hence, a lens module is driven by Lorenz Force that flows through the coil.
Thus, the camera module of the voice coil motor type uses a scheme of obtaining a position of a lens module in a manner of applying a drive signal to a coil and then sensing an induced current through a coil sensor. Since the camera module does not use such parts as a hole sensor, magnet and the like comparison with an existing hole sensor applied technology, it is advantageous in material cost reduction, manufacturing process simplification and product downsizing.
However, regarding the camera module of the voice coil type, when a sensing signal for sensing a moving position of a lens module is received, since noise is generated due to effects of an OIS (optical image stabilizer) signal, a drive signal for a movement of the lens module and the like, it causes a problem that the moving position of the lens module cannot be sensed accurately.
Thus, the camera module has a problem that an accurate position of the lens module cannot be accurately measured due to the noise generated from the sensing signal.